a) Field of the Invention
The invention is directed to a process for the production of white and black oxide ceramic surface films on silicon-containing light metal cast alloys by means of plasma-chemical anodic oxidation.
b) Background Art
It is known to produce high-adhesion, dense and thick dispersion films on metals, especially on iron and iron work materials, by means of anodic arc-discharge or conventional thermal treatment by deposition from dispersion systems (DD-PS 151330).
The disadvantage in this solution consists in that
a constant stirring of the suspension must be carried out to prevent the precipitation of the dispersion suspension; PA0 a subsequent annealing must be effected at 900.degree. after depositing the films so that the process is unsuitable for light metals; PA0 no data are indicated in the patent concerning adhesion strength. PA0 there is either no data concerning the utilized electrolytes DD 151 331; PA0 or that all electrolytes contain fluoride and accordingly raise problems with respect to disposal; PA0 there are no concrete data concerning adhesion strength of the produced film - PS DD 142 360, DD 218 637; PA0 only a decreased adhesion strength can be expected due to the occurrence of a "grainy" surface - PS DD 142 360, PA0 there are no data concerning resistance to corrosion or the produced film - PS-DD 209 661, DD 218 637; PA0 and costly secondary treatments place higher demands on the production technology. PA0 degreasing with conventional degreasing agents or in an ultrasonic bath; PA0 pickling in 10-20-percent caustic soda lye (NaOH) PA0 passivation in 10-percent nitric acid (HNO3) PA0 rinsing in distilled water between each process step. PA0 DD 235 442--treatment of the aluminum surface with a mixture of a water glass solution MgO, CaO, NaOH and water for producing an adhesive base for pur [polyurethane]-coating systems; PA0 DD 239 927--two-step etching processes for eliminating lattice imperfections due to mechanical isolating processes and for defined surface roughening in A.sub.III -B.sub.v -semiconductor components by PA0 1. polishing treatment in a solution of phosphoric acid, hydrogen peroxide and water; PA0 2. etching for uniform texturing in phosphoric acid, hydrogen peroxide or sulfuric acid and hydrogen peroxide; PA0 DD 251 905--improvement of the adhesive and contact behavior of metal films on p+-conductivity zones of A.sub.III - B.sub.v -semiconductor components by treating the surface with etching baths consisting of: PA0 a mixture of hydrofluoric acid, hydrogen peroxide and water and a second mixture of sulfuric acid, hydrogen peroxide and water; PA0 DE-OS 34 05 437--alkaline bath for decorative etching of aluminum and its alloys comprising sodium hydroxide NaOH, sodium carbonate Na.sub.2 CO.sub.3, sodium tripolyphosphate Na.sub.5 P.sub.3 O.sub.10, potassium hydroxide Ca(OH).sub.2, copper fluoride CuF.sub.2, sodium nitrate NaNO.sub.3 and sodium nitrite NaNO.sub.2 ; PA0 DE-OS 35 37 584--process and apparatus for preventing corrosion after carrying out plasma etching on aluminum, wherein SiCl.sub.2, Cl.sub.2 and AlCl.sub.3 are formed individually or together; PA0 GB 8 227 118--cleaning of aluminum surfaces to be anodized by means of hexafluorophosphoric acid II [PF.sub.6 ] and possibly nitric acid HNO.sub.3 ; PA0 U.S. Pat. No. 359 339--process for electrochemical roughening of aluminum or its alloys in an aqueous electrolyte comprising nitric acid, oxalic acid and possibly additions of boric acid, aluminum nitrate and/or hydrogen peroxide. PA0 they are not suitable for the selective etching of the respective surface and accordingly cannot be used for pretreatment and the preparation of the surface for a plasmachemical anodic oxidation on light metal cast alloys incident thereto; PA0 and they sometimes involve very costly devices and process steps; PA0 the pretreatment, e.g. in DD-PS 235 442, is not sufficient for producing protective layers with high adhesive strength. Such protective layers have the disadvantage of a low service life and have short maintenance cycles with susceptibility to corrosion resulting in warping and tearing. PA0 that no reproducible roughening of the surface is possible PA0 and that there is a precipitation of decomposition products on the surface. PA0 dry processes such as PA0 the surface to be etched must undergo a costly pretreatment prior to the actual, possibly selective etching process, e.g. the surface is coated with an organic resist, irradiated and developed at certain places. This results in a resist mask which exposes certain surface areas which are etched in the subsequent work step; PA0 in a bombardment with high-energy particles, radiation damage such as lattice imperfections, which impede or prevent further processing of the etched surface, can occur in the remaining material; PA0 in that a high resist erosion occurs, likewise as a result of the aforementioned bombardment; PA0 and in that there is unwanted etching of a layer of the body situated below the layer to be etched or disturbing undercuts. PA0 wet-chemical etching processes PA0 no exact compositions of the etching agent are indicated to some extent; PA0 the "etching" process step is implemented only in apparatuses of complicated construction; PA0 and material is removed only over the entire surface of the work material to be etched; PA0 in that consequently no strictly controllable etching profiles can be provided; PA0 and in that extensive masking work must be carried out for a possible selective etching. PA0 DD-PS 208 886--selective etching of phosphorous-doped silicon films in a hydrofluoric acid containing etching medium, wherein the silicon dioxide films must be tempered in a hydrogen atmosphere at 600 to 1000.degree. C. to reduce the high etching rate; PA0 DD-PS 238 622--selectively acting etching agents for etching doped silicon dioxide or silicon glass films. This etching agent comprises hydrofluoric acid and an organic solvent of low polarity which can be mixed with water, preferably dioxane. Concrete data on the selectivity of the etching rate of the etching agent and for the selective removal of the silicon surfaces are not indicated. PA0 DD-PS 206 168--etching agent for structuring polycrystalline silicon films comprising a mixture of acetic acid, hydrofluoric acid, nitric acid, water, silver nitrate and a catalytic amount of nitrite ions. Here also there is no concrete data on the selectivity of the etching rate of the etching agent and for the selective removal of the polycrystalline silicon surfaces. PA0 U.S. Pat. No. 793 402--etching solution and etching process for doped silicon comprising hydrofluoric acid, nitric acid or acetic acid. Again, there are no data on the etching rate selectivity of the etching agent. PA0 DD-PS 249 706--etching agent for etching silicon dioxide or silicon dioxide-containing glasses on semiconductor materials which are partially covered with aluminum. The etching agent comprising a sodium salt, a diluted hydrofluoric acid, and a cationic surface-active tenside is supposed to prevent the removal of the aluminum during the SiO2 etching. This solution is disadvantageous in that this form of structuring of silicon dioxide is selective, but not sufficient for preparing the work material for further processing, e.g. the plasma-chemical anodic oxidation for producing oxide ceramic surface films on light metal cast alloys. PA0 a removal of material is fundamentally effected over the entire surface of the work material with the wet-chemical etching process; PA0 extensive pretreatments in the form of masking processes must be carried out in part in order to enable a selective etching; PA0 a selective etching without masking processes is possible in certain cases, but no controllable etching profiles can be produced; PA0 and such variants of etching are inadequate for further processing of the work material with respect to its qualitative parameters, e.g. with respect to the production of oxide ceramic films by means of plasma-chemical anodic oxidation on light metal cast alloys.
The patents DD 142 359, DD 142 360, DD 151 331, DD 205 197, DD 209 661 and DD 218 637 describe processes for the production of oxide films on aluminum work materials or bonds on aluminum work materials by means of ANOF processes. A disadvantage in these processes, as in those listed above, consists in that
PS DE 17 711 A1 describes an electrolyte for producing high-adhesion, deep-black conversion films on light metals or their alloys which are realized by means of ANOF processes. Also, electrolytes for the production of extremely thin black conversion films and electrolytes for producing white, thermal-shock-resistant, high-adhesion, oxide ceramic surface films on light metals and their alloys which are likewise realized by means of plasma-chemical anodic oxidation have become known recently.
The significant disadvantage of all these listed solutions consists in that they are not suitable as variants for providing films on light metal cast alloys by means of plasma-chemical anodic oxidation.
It is likewise known from the technical literature as described e.g. in Pocketbook for Galvanic Technology [Taschenbuch fur Galvanotechnik], volume 1, Process Technology [Verfahrenstechnik], 13th edition 1988, LPW-Chemie GmbH, W-4040 Neuss) to produce thin oxide films on aluminum work materials, also including aluminum cast alloys, by means of electrochemical anodic oxidation, especially eloxing processes. This method requires the following process steps e.g. for preparing aluminum cast alloys for anodic oxidation:
A disadvantage in these coating variants consists in that they are unsuitable for producing thin uniform oxide films particularly on structural component parts having complicated shapes. The use of such coating variants is therefore very limited and therefore basically inadequate in optical precision equipment construction.
Further, the following solutions for the pretreatment of surfaces of aluminum work materials are known from the patent literature:
Common to all of these solutions is that:
DE-OS 27 30 953 describes a wet-chemical etching process for producing highly roughened surfaces, but which has the disadvantage that additional under-etchings at the edge areas, e.g. edge undercuts, are brought about which favor mechanical destruction processes during further processing.
U.S. Pat. No. 40 94 752 describes a wet-chemical etching process by means of an etching solution based on HF and HNO.sub.3. In this case the following disadvantages should be mentioned particularly:
A number of different processes are known from the patent literature for the pretreatment of surfaces of chiefly siliconcontaining work materials:
plasma etching; U.S. Pat. No. 730 988, DE-OS 36 27 311, DE-OS 29 30 290, DE-OS 29 30 293, U.S. Pat. No. 39 40 504, U.S. Pat. No. 40 69 096, DE-OS 34 20 347 PA1 ionic etching, DE-OS 30 45 922 PA1 cathodic atomization and the like. PA1 U.S. Pat. No. 8 75 833--etching solution and process for etching silicon by means of ethanolamine, piperidine, H.sub.2 O, pyrocatechol and H.sub.2 O.sub.2 ; PA1 DE-OS 29 50 54--cleaning of the surfaces of silicon plates by means of hydrofluoric acid; PA1 JP-PS 139 620/84--etching of a polycrystalline silicon film by means of nitric acid and hydrogen peroxide; PA1 U.S. Pat. No. 637 874--production of an electronically passivating surface on crystalline silicon by means of hydrofluoric acid and an organic upper layer in an atmosphere of inert gas.
The disadvantages of these processes particularly consist in that
These solutions are disadvantageous in that
Further, processes for selective etching of silicon films are known from the patent literature:
The disadvantage of all of the listed solutions in addition to those disadvantages already listed consists in that